Windows Xp wont boot up

My HP Notebook starts up ok and then the windows page loads and the moving dots moving back and forwards in the bar and then the screen goes blank and it shuts down and starts back up again going round in a circle.

Systems do this if the os hasnt been registered within the time limit or you could have missing sys files either way you'll have to re-install windows either repair existing os or fresh install..I suggest fresh install....you could try booting to safe mode then restart using option start with last known config that worked..you could even try startup from usb to get to dos prompt(virtual dos)
and type in win and enter or type first "chkdsk"which if successful will check and repair any errors;but if they all fail and quite possibly they will you'll need to reinstall anyway.

Try starting windows in safe mode and go to an earlier system restore point if that wont work try installing windows again if windows wont respond to this it will be a hard drive issue it will need replacing

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1. Press F8 as it's booting and select 'go back to last working configuration'
if that doesn't work, go to step 2.
2. Press F8 as it's booting, and choose 'Launch startup repair' (I'm assuming you have Vista/Windows 7).
If your on XP, you need to do a windows repair which is described here: http://www.michaelstevenstech.com/pdf/XPrepairinstall.pdf

Try start up in Safe Mode press F8. Choose Safe Mode, when at the choice window, to select either Safe Mode Desktop, OR System Restore, chooses system restore and choose a time before you had the "Problem" and follow instructions. This should get you back.

I'm guessing ou have windows XP?if so you hae a corrupted regisry and need to boot from your Windows CD and at he first et of questions choose Eneter to intall windows, then F8 to continue and then it should tell yo another Windows insatallation has been found and ask if you wish to perform an automatic repair.